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remaining surface contaminants may be transported to the first saturated zone of the <br />aquifer. <br />First ground water is predicted at 145 to 153 feet below ground surface for this Site; <br />consequently, significant nitrate reduction would be anticipated as the septic effluent <br />percolates downward. <br />Sources of Nitrate <br />Dairies, orchards that require fertilization in sandy soils, and septic systems have been <br />found to be the most significant sources of nitrate in ground water. <br />Percolating Recharge Waters <br />One of the most determinant factors in the Hantzsche and Finnemore equation is the <br />rate of recharge from percolating waters, which mix with the downward-percolating <br />effluent generated by on-site septic systems. In the original Hantzsche and Finnemore <br />paper, only "average recharge rate of rainfall" was considered. For the Chico area, <br />Hantzsche and Finnemore present an average rainfall of 22.5 inches per year and an <br />estimated recharge of 16.8 inches per year. <br />Based on San Joaquin County Environmental Health Department policy (personal <br />communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore <br />equation should be derived from average monthly precipitation of rainfall and <br />evapotranspiration rates for the area; the data should be obtained from the California <br />Irrigation Management Information System (CIMIS). Recharge is calculated by first <br />determining whether the average monthly precipitation exceeds average monthly <br />potential evapotranspiration. If so, then the difference is the percolating recharge water <br />into the aquifer. Runoff and stream infiltration drainage are not factored into the <br />calculation. This approach likely under-estimates recharge to the aquifer and, <br />consequently, over-estimates nitrate loading. <br />For the project Site, the local percolation and evapotranspiration rates are presented in <br />Plate 15. The closest CIMIS station to the Site is Staten Island (station 242). Data for <br />the Staten Island station were available for the past three years; based on the <br />calculation shown, the estimated rate of recharge from percolating waters for the Staten <br />Island station is determined to be 12.60 inches (Plate 15). A statistical error of 49% is <br />associated with this value. <br />Quality of Rainwater <br />Hantzsche and Finnemore listed 1 mg/L-N as the nitrate concentration of rainwater for <br />their original calculation; in the past, Live Oak has also utilized this value for the nitrate <br />loading calculation. <br />LOGE 1850 Page 10